Generally, when used with circuitry operating a spatial light modulator, a color wheel used for generating high quality color images on a display has a single index mark that is sensed and used to synchronize the phase and speed of the color wheel with an image frame sync pulse. More specifically, a spatial light modulator, such as for example, a DMD™ (digital micromirror device) spatial light modulator available from Texas Instruments Incorporation in Dallas, Tex., uses such a color wheel.
The very high operating speed of the DMD™ and the continuous demand for higher and higher quality color images emphasizes the need for color wheels with extremely stable speed and phase control. More specifically, because of the high rotational speed of a color wheel and the high color cycle rate needed for high quality color images, a color wheel that is rotating at a slightly incorrect speed or that is only slightly out of phase may be producing one color when the system is expecting another color.
Therefore, to avoid such problems, speed and phase correction of the color wheel are now needed to compensate for speed and/or phase variations that occur during a single revolution of the color wheel. Prior attempts to provide such minute control of the color wheel have been attempted by simply increasing the number of index marks on the color wheel so that the control circuitry will receive an index or event pulse at a more frequent rate. For example, if four index marks are evenly placed around the color wheel, the control circuitry can detect a speed or phase variation four times faster than with a single index mark. This would appear to be a simple and good solution, but unfortunately because it is very difficult to precisely space the index marks evenly around the wheel, the addition of index marks may not provide any improvement. Attempts to average the timing of the index marks or to calibrate the circuitry to compensate for these placement errors have not been particularly successful.
Therefore, it would be advantageous to produce synchronization apparatus and methods that would automatically and accurately compensate for the non-periodic arrival of index events or signals such as caused by placement errors of the index marks on a color wheel.